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RESEARCH ARTICLE Open Access

Change in adduction moment followingmedial open wedge high tibial osteotomy:a meta-analysisJun-Ho Kim1†, Hyun-Jung Kim2†, Haluk Celik3, Joo-Hwan Kim1 and Dae-Hee Lee1*

Abstract

Background: This meta-analysis was designed to quantify adduction moment loss, to evaluate the relationshipbetween changes in mechanical axis alignment and adduction moment, and to assess whether sagittal planemoment is altered after medial open wedge high tibial osteotomy (HTO).

Methods: Following preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, allstudies reporting preoperative and postoperative peak knee adduction moment or change in peak knee adductionmoment from before to after surgery in patients who underwent medial open wedge HTO were included.

Results: Nine studies were included in the meta-analysis. The pooled mean difference in adduction moment frombefore to after medial open wedge HTO was 1.44% Nm/body weight (BW)xheight (HT) (95% confidence interval [CI]:1.33 to 1.55% Nm/BWxHT; P < 0.001; I2 = 4%). However, flexion (0.18% Nm/BWxHT, 95% CI: -0.50 to 0.86% Nm/BWxHT;P = 0.61; I2 = 79%) and extension (0.15% Nm/BWxHT, 95% CI, − 0.37 to 0.68% Nm/BWxHT; P = 0.56; I2 = 46%) momentsdid not differ significantly from before to after surgery. Alignment correction amount and postoperative final valgusalignment were not significantly associated with difference in adduction moment from before to after surgery.

Conclusion: Knee adduction moment after medial open wedge HTO decreased to 60% of the preoperative level.However, this adduction moment decrement was not affected by the magnitude of alignment correction. In addition,there was no change in sagittal plane knee moment, including flexion and extension moments, from before to aftermedial open wedge HTO.Level of Evidence: Meta-analysis (Level II).

Keywords: Adduction moment, Alignment, Knee, Open wedge high tibial osteotomy

BackgroundMedial open wedge high tibial osteotomy (HTO) is anestablished procedure for medial compartment osteo-arthritis in relatively young active patients [1]. The keyto success of HTO is the magnitude of correction, whichinfluences load distribution borne by the knee joint [2].Load distribution on the knee joint can be determinedstatically by radiographic measurements of mechanicalaxis alignment and dynamically by measuring the adduc-tion moment [3]. Adduction moment is defined as themagnitude of the ground reaction force (GRF) passing

medial to the knee joint center during gait and the mo-ment arm of the GRF. Knee adduction moment is anindicator of dynamic mechanical load on the knee jointand increases in proportion to knee varus deformity.Although adduction moment has been reported to pre-dict the progression of medial compartment osteoarth-ritis, there is no general consensus about the magnitudeof adduction moment reduction after medial openwedge HTO [4]. Theoretically, the magnitude of thecorrection in mechanical axis alignment may be closelyassociated with the change in adduction moment, butprevious studies yielded conflicting results regarding therelationship between these two parameters [5, 6]. Inaddition, although medial open wedge HTO can affectthe biomechanical moment in the sagittal plane due to

* Correspondence: [email protected]†Jun-Ho Kim and Hyun-Jung Kim contributed equally to this work.1Department of Orthopaedic Surgery, Samsung Medical Center,Sungkyunkwan University School of Medicine, Seoul, KoreaFull list of author information is available at the end of the article

© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Kim et al. BMC Musculoskeletal Disorders (2019) 20:102 https://doi.org/10.1186/s12891-019-2472-9

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unintended changes in posterior tibial slope, little isknown about the change in sagittal plane moment aftermedial open wedge HTO [7]. This meta-analysis wasperformed to quantify adduction moment loss, to deter-mine the relationship between change in mechanical axisalignment and change in adduction moment, and toassess whether the sagittal plane moment is altered aftermedial open wedge HTO. It was hypothesized that thedecrement in adduction moment is closely associatedwith the magnitude of correction in mechanical axisalignment, and that medial open wedge HTO alters thebiomechanical environment of the knee joint, not onlyin adduction moment on the coronal plane but also inflexion and/or extension moments on the sagittal plane.

MethodsLiterature searchThe present meta-analysis was performed in accordancewith the guidelines of the preferred reporting items forsystematic reviews and meta-analysis (PRISMA) state-ment and Cochrane Review methods. Comprehensivedatabases, including EMBASE, PubMed, and theCochrane Library were sought for studies comparing thepre- and postoperative adduction moment of the kneejoint in the patients who underwent open wedge HTOup to May 2018. No restrictions were considered forlanguage or year of publication. Search terms including“Osteotomy” [tiab] OR “Tibial” [tiab] OR “High” [tiab]OR “Open” [tiab], AND “Osteotomy” [MeSH] OR “ad-duction moment” [tiab] were sought in the title, abstract,MeSH, and keyword fields. Manual searches wereadditionally done to detect articles potentially missed bythe electronic search.

Study selectionThe titles and abstracts of the selected studies were eval-uated by two reviewers, independently. If enough datawere not obtained using the abstract, the full text of thearticle was reviewed. Studies were included according tofollowing conditions: (1) preoperative and postoperativepeak knee adduction moment or change in the peakknee adduction moment between prior to and aftersurgery in the patients who underwent medial openwedge HTO were reported; (2) primary outcomes in-cluded change in the peak knee adduction moment,standardized to body weight (BW) and height (HT); and(3) the numbers of samples included in the final analysiswith means and standard deviations of adductionmoment. Studies were excluded if (1) they reported onlyeither preoperative or postoperative adduction moment;or (2) they did not include appropriate information, suchas standard deviation or range of values.

Data extractionData was extracted from each study by two authorsusing a data extraction form. A third author reviewedthe data in case of any disagreement.The variables were noted as following: (1) mean and

standard deviations of the peak adduction moments ofthe knee joint and mechanical axis alignment before andafter medial open wedge HTO; (2) sample size; and (3)study type (e.g. prospective or retrospective comparisonstudies). In case of the absence of the variables, thecorresponding author of the related study was asked toprovide the necessary data via e-mail. The correspondingauthors of two studies responded our requests andshared the necessary information.

Assessment of methodological qualityThe Newcastle-Ottawa Scale was used to define themethodological qualities of each study by two reviewers,independently [8], as recommended by the CochraneNon-Randomized Studies Methods Working Group.The Newcastle-Ottawa Scale includes the followingcriteria: the comparability of the groups, the definitionof the study groups and the cohort studies identificationof either the exposure or outcome of interest for case–control or. Studies had scores > 5 points determined as ahigh quality study. Disagreements related to the scores be-tween reviewers were solved by discussion and consensus.

Statistical analysisMean differences in the peak knee adduction momentsprior to and after medial open wedge HTO were themain outcomes of the meta-analysis. Random-effectsmeta-analyses were implemented to collect these out-comes through included studies, by estimating theweighted mean differences, and 95% confidence intervals(CIs). To define the heterogeneity among studies, I2

statistics was used by estimating the amount of irregu-larities due to actual differences between studies, ratherthan differences due to random error or chance. Thevalues of 25, 50, and 75% were considered as low,moderate, and high, respectively.Statistical analysis was performed using RevMan

version 5.2 (Copenhagen, the Nordic Cochrane Centre,The Cochrane Collaboration, 2012). The risks of biaswere independently assessed by two investigators andwere indicated as either low, high or unclear.A random-effects meta-regression was used by assum-

ing that the true effects follow a normal distributionaround the linear predictor.A meta-regression analysis was performed to evaluate

the influence of alignment correction amount and postop-erative alignment on change of adduction moment frombefore to after high tibial osteotomy. The permutation testbased on Monte Carlo simulation was conducted to adjust

Kim et al. BMC Musculoskeletal Disorders (2019) 20:102 Page 2 of 7

the risk of false-positive findings with multiple covariatesusing few studies.

ResultsIdentification of studiesFigure 1 presents the details of study identification,inclusion, and exclusion. An initial electronic searchyielded 358 studies in PubMed (MEDLINE), 509 inEMBASE, 382 in Web of Science, 503 in SCOPUS, and22 in the Cochrane Library. In additon, four studies wereidentified through manual searching. Once 705 dupli-cates were eliminated, 1051 of the remaining 1072studies were excluded based on reading of the abstractsand full-text articles. An additional 12 studies wereexcluded due to the absence of the usable informationor usage of only either preoperative or postoperativepeak adduction moment measuraments. Consequently,nine studies [5, 6, 9–15] were included in the presentmeta-analysis.

Study types and methodological quality of the includedstudiesThe final nine studies compared the adduction momentin subjects prior to and after medial open wedge HTO.Flexion and/or extension moments were also compared

prior to and after the surgery in five of those. Allincluded studies presented low risk of selection bias.Sufficient follow-up duration was defined as the timeinterval between surgery and performance of gait ana-lysis, with a shorter time interval associated with ahigher risk of bias, due to accurate measurement ofadduction moment being unlikely. All included studiesincluded the patients with medial compartment kneeosteoarthritis who underwent open HTO with fixationof locking plate. The patient demographic such as ageand gender ratio were also similar between studies.These findings could suggest the lower risk of bias forrepresentativeness of cases in each study. Four of eightstudies had a high quality level (> 5 points) according tothe Newcastle-Ottawa Scale (Table 1).

Adduction moment change after medial open wedgeHTOA total of 462 knees that underwent medial open wedgeHTO were evaluated. The pooled mean difference inadduction moment prior to and after medial open wedgeHTO was 1.44% Nm/BWxHT (95% CI: 1.33 to 1.55%Nm/BWxHT; P < 0.001; I2 = 4%) (Fig. 2). The adductionmoment was reduced by roughly 40% of preoperative

Fig. 1 PRISMA (Preferred Reporting Items for Systematic reviews and Meta-analyses) flow diagram of the identification and selection of thestudies included in this meta-analysis


levels (mean preoperative adduction moment 3.46%Nm/BWxHT).

Changes in flexion and extension moment after medialopen wedge HTOOf the eight studies, four reported changes of flexionand extension moments in the sagittal plane as well aschanges in adduction moment in the coronal plane.Slight mean differences in flexion (0.18 Nm/BWxHT,95% CI: -0.50 to 0.86% Nm/BWxHT; P = 0.61; I2 = 79%,Fig. 3) and in extension (0.15 Nm/BWxHT, 95% CI:-0.37 to 0.68% Nm/BWxHT; P = 0.56; I2 = 46%, Fig. 4)moments were observed, but neither was statisticallysignificant.

Meta-regression analysesThe results of meta-regression analyses are reported inTable 2. Alignment correction amount and postoperativefinal valgus alignment were not significantly associatedwith difference in adduction moment from before to

after surgery. This finding indicated that the change inadduction moment from before to after medial openwedge HTO was not influenced by the magnitude ofalignment correction or postoperative final valgusalignment. Monte Carlo permutation test was also usedto confirm the false positive findings due to smallsample size of our including studies. The results of thistest also showed no significant association between age(P = 0.466) and follow up (P = 0.149) and adductionmoment change from before to after medial open wedgeHTO.

DiscussionThis meta-analysis verified that knee adduction momentdecreased markedly after medial open wedge HTO,reaching about 60% of the preoperative level, whereasknee flexion and extension moments were not altered bysurgery.The mechanical force loaded onto the knee joint in

patients with medial osteoarthritis and varus deformity

Table 1 Characteristics and quality of studies included in the meta-analysis

Author Year StudyType

SampleSize, n

Male/FemaleSex, n

MeanAge, y

MeasuredParameters

Time fromsurgery tomeasurement,mo

Follow-up,Mean, mo

Mechanical axis angle, degrees QualityscoreBaseline

Mean (SD)Final assessmentMean (SD)

Birminghamet al. [9]

2009 PCS 126 102 47.48 ADM 24 24 −8.00 (4.09) −0.05 (3.05) 5

DeMeo et al. [10] 2010 PCS 20 14 49.4 ADM 7.2 99.6 −3.6 (N/R) 7.5 (N/R) 6

Kean et al. [11] 2009 RCS 21 N/R 38.9 ADM, FLM, EXM 12 12 −6.03 (3.29) 0.33 (N/R) 8

Leitch et al. [12] 2015 RCS 14 12 48 ADM, FLM, EXM 12 12 −7.61 (N/R) 0.52 (N/R) 6

Lind et al. [5] 2013 RCS 11 11 46 ADM, FLM, EXM 12 12 −8 (2.8) 0 (2.1) 7

Marriot et al. [13] 2015 PCS 33 N/R 40 ADM, FLM, EXM 60 68 −5.90 (2.87) 1.69 (2.37) 4

McClelland et al. [6] 2016 RCS 36 33 54.11 ADM 72 72 −8.6 (0.88) −1.44 (1.05) 6

Sischek et al. [14] 2014 RCS 37 29 49.3 ADM 6 48 N/R −8.35 (3.33) 1.25 (2.67) 8

Birminghamet al. [15]

2017 PCS 170 135 46.4 ADM, FLM 60 60 −8.01 (3.38) 0.28 (2.86) 7

PCS prospective comparison study, RCS retrospective comparison study, ADM adduction moment, FLM flexion moment, EXM extension moment, N/R not reported;For mechanical axis angle, negative values indicate varus alignment

Fig. 2 Forest plots of studies showing the change of adduction moment in patients who underwent medial open wedge high tibial osteotomy


is an important predictor of osteoarthritis progression.Although the mechanisms by which increased mechan-ical loading adversely affects cartilage are unclear, theymay involve chondrocyte death, disruption of the extra-cellular matrix, and microfracture within the subchon-dral cortical endplate. Knee adduction moment is asurrogate measure of dynamic mechanical load on theknee joint and increases in proportion to knee varusdeformity. The success of medial open wedge HTOdepends not only on alignment correction but also ondecreasing the adduction moment, thereby reducing themechanical load on the medial compartment of theknee. Determining the magnitude of adduction momentloss and its clinical relevance after medial open wedgeHTO is therefore important. This meta-analysis showedthat medial open wedge HTO reduced preoperativeadduction moment by about 40%. One recent studyreported that a 1% increase in adduction moment in-creased the risk of progression of knee osteoarthritis6-fold. These findings suggest that a 40% reduction inadduction moment would delay the progression of med-ial osteoarthritis. Another recent study found that theload on the medial compartment while walking increases5% for every 1° change towards varus [16]. Our studyfound that the magnitude of alignment correction wasnot significantly related to the reduction in adductionmoment. Nevertheless, because the mean amount ofcorrection following medial open wedge HTO in thestudies included in this meta-analysis was approximately8°, the 40% reduction in adduction moment comparedwith the preoperative level may be explained by the

results showing a 5% decrease in adduction moment per1° change towards varus.The knee adduction moment is a consequence of the

magnitude of the ground reaction force (GRF) passingmedial side of the center of the knee joint during gaitand the moment arm of the GRF, and defined as theperpendicular distance from the GRF to the center ofthe knee joint [17]. Therefore, the mechanical axis andknee adduction moment are positively correlated witheach other [18]. In contradiction to that knowledge, theresults of our meta-analysis revealed an absence of asso-ciation between the magnitude of alignment correctionand/or the degree of valgus and the reduction in adduc-tion moment following medial open wedge HTO.Several causes are possible. First, despite the largeamount of the correction, the mechanical axis may nothave reached to the ultimate end-point, which was62.5% of the width of the entire tibial plateau. Second,the adduction moment may have been affected by otherfactors except the mechanical axis alignment. Forinstance, in spite of the fact that the mechanical axis wasshown as an indicant of the peak adduction moment, itonly accounted for roughly 50% of the variation in thepeak adduction moment [19]. The foot progressionangle, lateral trunk tilt, knee flexion angle, and walkingspeed may also affect knee adduction moment. Increasedlateral trunk tilt and out-toeing gait may decrease theknee adduction moment, whereas bigger knee flexionangle and higher walking speed have been reported asfactors that may increase the knee adduction moment[18, 20, 21]. In addition, the strength of extensor and

Fig. 3 Forest plots of studies showing the change of flexion moment in patients who underwent medial open wedge high tibial osteotomy

Fig. 4 Forest plots of studies showing the change of extension moment in patients who underwent medial open wedge high tibial osteotomy


flexor muscles of the knee and the knee joint laxityaffect the adduction moment [22–24].Medial open wedge HTO can affect the sagittal plane

moments of the knee during gait. Sagittal planemoments may alter the mechanical load borne by themedial compartment of the knee joint. Previous studiesshowed conflicting results for change in flexion moment.One study showed increased flexion moment after HTOdue to increasing gait speed and flexion angle, andimproved quadriceps function resulting from reducedpain following HTO [5]. In contrast, another studyfound that not only peak adduction moment but alsoflexion moment were reduced 12months after medialopen wedge HTO [12]. Our meta-analysis showed nosignificant change in either flexion or extension mo-ment. Differences between study results may be due tothe small effect on the sagittal plane of the magnitude ofcorrection of mechanical axis alignment, despite thechange in mechanical axis alignment being closelyassociated with change in adduction moment after med-ial open wedge HTO. Neuromuscular changes, whichwidely vary among individuals and are unpredictable,may contribute to changes in sagittal plane moments[24]. An unintended posterior slope of the articularsurface of the proximal tibia in the sagittal plane mayalso affect changes in sagittal plane moments. However,a recent meta-analysis showed that the magnitude ofincrease in the posterior tibial slope following medialopen wedge HTO was only 2°, suggesting that this slightchange may have little effect on the biomechanical envir-onment of the knee joint [25]. The results of that studymay explain, at least in part, the lack of significantchange in sagittal plane moments observed in our study.This study had several limitations. Although adduction

moment is a proxy measure of the mediolateral distribu-tion of loads across the knee, it is not a direct measureof the actual force borne by the knee joint. The angularimpulse of knee adduction moment was shown to be amore comprehensive indicator of cartilage volume re-duction in osteoarthritis than peak knee adduction mo-ment [4], because the former accounts not only for loadmagnitude but also load duration, which contribute tototal knee load exposure [26]. However, angular impulseof adduction moment has only recently been measured,making peak knee adduction moment a more practicalmeasure, as well as being a valid and reliable dynamic

indicator of compressive load in the medial compart-ment during walking and a useful parameter for compar-ing the results of studies that assess adduction moment.Another limitation was the variation in preoperativemechanical axis and lateral thrust among includedstudies, which may have resulted in large variations indata, including adduction moment, during gait. Thisfinding may also be a potential cause of heterogeneity inthis meta-analysis [22]. Finally, a meta-regressionanalysis, which performed in this study to investigate theinfluence of alignment correction amount and postoper-ative alignment on change of adduction moment, wasalso prone to instability in the results due to relativelysmall sample size.

ConclusionsKnee adduction moment after medial open wedge HTOdecreased to 60% of its preoperative level. However, thisadduction moment decrement was not affected by themagnitude of alignment correction. In addition, therewas no change in sagittal plane knee moment, includingflexion and extension moments, from before to aftermedial open wedge HTO.

AbbreviationsBW: Body weight; CI: Confidence interval; HT: Height; HTO: High tibialosteotomy; PRISMA: Preferred reporting items for systematic reviews andmeta-analysis

AcknowledgementsWe would like to thank all the people who helped us in the current study.

FundingThis study was supported by SMC-Ottogi Research Fund (SMX1162171). Thefunding agency was not involved in any aspects of the study design, includ-ing data collection, interpretation of data or manuscript preparation.

Availability of data and materialsAll data generated or analyzed during this study are included in thispublished article.

Authors’ contributionsMade substantial contributions to conception and design, or acquisition ofdata: KJH and CH; Analysis and interpretation of data: KJH, KHJ, CH, KJH, andLDH; Been involved in writting the manuscript: KJH, KHJ, CH, KJH, and LDH;Each author should have participated sufficiently in the work to take publicresponsibility for appropriate portions of the content and all authors haveread and approved the manuscript.

Ethics approval and consent to participateNot applicable.

Table 2 Meta-regression analyses between correction amount and postoperative valgus, and change in adduction moment frombefore to after medial open wedge high tibial osteotomy (HTO)

Variable Coefficient Standard error P value 95% confidence interval

Change in adduction moment from before to after surgery

Correction amount −0.180 0.096 0.159 −0.487 to 0.127

Postoperative valgus −0.012 0.037 0.767 −0.106 to 0.130


Consent for publicationNot applicable.

Competing interestsThe authors declare that they have no competing interests.

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.

Author details1Department of Orthopaedic Surgery, Samsung Medical Center,Sungkyunkwan University School of Medicine, Seoul, Korea. 2Department ofPreventive medicine, Korea University College of Medicine, Seoul, SouthKorea. 3Department of Orthopaedic Surgery, Umraniye Training and ResearchHospital, Istanbul, Turkey.

Received: 4 June 2018 Accepted: 21 February 2019

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http://www.ohri.ca/programs/clinical_epidemiology/oxford.htmhttp://www.ohri.ca/programs/clinical_epidemiology/oxford.htm

AbstractBackgroundMethodsResultsConclusion

BackgroundMethodsLiterature searchStudy selectionData extractionAssessment of methodological qualityStatistical analysis

ResultsIdentification of studiesStudy types and methodological quality of the included studiesAdduction moment change after medial open wedge HTOChanges in flexion and extension moment after medial open wedge HTOMeta-regression analyses

DiscussionConclusionsAbbreviationsAcknowledgementsFundingAvailability of data and materialsAuthors’ contributionsEthics approval and consent to participateConsent for publicationCompeting interestsPublisher’s NoteAuthor detailsReferences

change in adduction moment following medial open wedge ......research article open access change in...

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